Angle resolved photoemission from Nd1.85Ce0.15CuO4 using high energy photons: a fermi surface investigation

We have performed an angle resolved photoemission study on a single crystal of the optimally electron doped (n-type) cuprate superconductor Nd2-xCexCuO4 (x=0.15) at a photon energy of 400 eV. The Fermi surface is mapped out and is, in agreement with earlier measurements, of hole-type with the expected Luttinger volume. However, comparing with previous low energy measurements, we observe a different Fermi surface shape and a different distribution of spectral intensity around the Fermi surface contour. The observed Fermi surface shape indicates a stronger electron correlation in the bulk as compared to the surface.     

Magnetic penetration depth measurements of Pr2-xCexCuO4-delta films on buffered substrates: evidence for a nodeless gap

We report measurements of the inverse squared magnetic penetration depth, lambda(-2)(T), in Pr(2-x)Ce(x)CuO(4-delta) (0.115< or =x < or =0.152) superconducting films grown on SrTiO3 (001) substrates coated with a buffer layer of insulating Pr2CuO4. lambda(-2)(0), T(c), and normal-state resistivities of these films indicate that they are clean and homogeneous. Over a wide range of Ce doping, 0.124< or =x < or =0.144, lambda(-2)(T) at low T is flat: it changes by less than 0.15% over a factor of 3 change in T, indicating a gap in the superconducting density of states. Fits to the first 5% decrease in lambda(-2)(T) produce values of the minimum superconducting gap in the range of 0.29< or =Delta(min)/k(B)T(c)< or =1.01.     

Nodal order parameter in electron-doped Pr(2-x)CexCuO(4-delta) superconducting films

The London penetration depth, lambda(ab)(T), is reported for thin films of the electron-doped superconductor Pr(2-x)Ce(x)CuO(4-delta) with varying Ce concentration, x=0.13, 0.15, and 0.17. Measurements down to 0.35 K were carried out using a tunnel-diode oscillator with excitation fields applied both perpendicular and parallel to the conducting planes. Films at all three doping levels exhibited power law behavior indicative of d-wave pairing with impurity scattering. These results are fully consistent with previous measurements on single crystals.     

Electron-phonon interaction at the Si(111)-7 x 7 surface

It is shown that electron-phonon interaction provides a natural explanation for the unusual band dispersion of the metallic surface states at the Si(111)-(7 x 7) surface. Angle-resolved photoemission reveals a discontinuity of the adatom band at a binding energy close to the dominant surface phonon mode at h(omega0) = 70 meV. This mode has been assigned to adatom vibrations by molecular dynamics calculations. A calculation of the spectral function for electron-phonon interaction with this well-defined Einstein mode matches the data. Two independent determinations of the electron-phonon coupling parameter from the band dispersion and from the temperature-dependent phonon broadening yield similar values of lambda = 1.09 and lambda = 1.06.     

Commensurate spin dynamics in the superconducting state of an electron-doped cuprate superconductor

We report neutron scattering studies on two single crystal samples of the electron-doped (n-type) superconducting (SC) cuprate Nd2-xCexCuO4 (x=0.15) with T(c)=18 and 25 K. Unlike the hole-doped (p-type) SC cuprates, where incommensurate magnetic fluctuations commonly exist, the n-type cuprate shows commensurate magnetic fluctuations at the tetragonal (1/2 1/2 0) reciprocal points both in the SC and in the normal state. A spin gap opens up when the n-type cuprate becomes SC, as in the optimally doped p-type La2-xSrxCuO4. The gap energy, however, increases gradually up to about 4 meV as T decreases from T(c) to 2 K, which contrasts with the spin pseudogap behavior with a T-independent gap energy in the SC state of p-type cuprates.     

Quantum and classical mode softening near the charge-density-wave-superconductor transition of CuxTiSe2

Temperature- and x-dependent Raman scattering studies of the charge-density-wave (CDW) amplitude modes in Cu(x)TiSe(2) show that the amplitude mode frequency omega(0) exhibits identical power-law scaling with the reduced temperature T/T(CDW) and the reduced Cu content x/x(c), i.e., omega(0) approximately (1-p)(0.15) for p=T/T(CDW) or x/x(c), suggesting that mode softening is independent of the control parameter used to approach the CDW transition. We provide evidence that x-dependent mode softening in Cu(x)TiSe(2) is associated with the reduction of the electron-phonon coupling constant, and that x-dependent "quantum" (T approximately 0) mode softening suggests the presence of a quantum critical point within the superconductor phase of Cu(x)TiSe(2).     

c-Axis optical sum rule and a possible new collective mode in La2-xSrxCuO4

We present the c-axis optical conductivity sigma(1c)(omega,T) of underdoped (x=0.12) and optimally doped (x=0.15) La2-xSrxCuO4 from 4 meV to 1.8 eV obtained by a combination of reflectivity and transmission spectra. In addition to the opening of the superconducting gap, we observe an increase of conductivity above the gap up to 270 meV with a maximal effect at about 120 meV. This may indicate a new collective mode at a surprisingly large energy scale. The Ferrell-Glover-Tinkham sum rule is violated for both doping levels. Although the relative value of the violation is much larger for the under-doped sample, the absolute increase of the low-frequency spectral weight, including that of the condensate, is higher in the optimally doped regime. Our results resemble in many respects the observations in YBa(2)Cu(3)O(7-delta).     

Evidence for a transition in the pairing symmetry of the electron-doped cuprates La(2-x)Ce(x)CuO(4-y) and Pr(2-x)Ce(x)CuO(4-y)

We present measurements of the magnetic penetration depth, lambda(-2)(T), in Pr(2-x)Ce(x)CuO(4-y) and La(2-x)Ce(x)CuO(4-y) films at three Ce doping levels, x, near optimal. Optimal and overdoped films are qualitatively and quantitatively different from underdoped films. For example, lambda(-2)(0) decreases rapidly with underdoping but is roughly constant above optimal doping. Also, lambda(-2)(T) at low T is exponential at optimal and overdoping but is quadratic at underdoping. In light of other studies that suggest both d- and s-wave pairing symmetry in nominal optimally doped samples, our results are evidence for a transition from d- to s-wave pairing near optimal doping.     

Behavior of the cholesteric liquid-crystal fabry-perot cavity in the bragg reflection band

In this Letter, we investigate the behavior of the cholesteric liquid-crystal Fabry-Perot cavity in the spectral range of the Bragg reflection band. We show that in this region the 2x2-Jones-matrix calculation gives a false predication. However, by the use of the 4x4-matrix method, interesting features are revealed in the resonance spectra. The resonance spectra split when lambda approximately &nmacr;P. Our experiments confirm this phenomenon. The experimental results show that the splitting occurs in a steplike fashion. This can be explained by the quantization of the pitch that occurs due to the fixed boundary conditions.     

Light-induced giant softening of network glasses observed near the mean-field rigidity transition

The longitudinal acoustic (LA) mode of bulk GexSe1-x glasses is examined in Brillouin scattering (BS) over the 0.15相似文献   

Interplay of externally doped and thermally activated holes in La(2-x)Sr(x)CuO4 and their impact on the pseudogap crossover

We presented the recent Hall effect data for a number of carriers in La(2-x)Sr(x)CuO4 as the sum of two components: the temperature independent term n0(x), which is due to external doping, and the thermally activated contribution. Their balance determines the crossover temperature T*(x) from the marginal Fermi liquid to pseudogap regime. The activation energy Delta(x) for thermally excited carriers equals the energy between the Fermi surface "arc" and the band bottom, as seen in angle-resolved photoemission spectroscopy experiments. Other implications for the (T, x)-phase diagram of cuprates are also discussed.     

α—NiSO4.6H2O晶体磁园二色谱和吸收谱的研究

用磁园二色谱和光吸收谱对α－ＮｉＳＯ４．６Ｈ２Ｏ晶体进行了测量和研究，实验结果表明在λ＝１８５～３３００ｎｍ范围内存在一系列吸收结构，其中三个主要主要吸收带结构分别对应于晶体中Ｎｉ离子基态到有关激发态的ｄ－ｄ跃迁，对它们进行了初步指认，实验中观测到红带的λ＝６５４ｎｍ和λ＝７１３ｎｍ两结构间存在一系列弱的结构峰，它们主要与自旋轨道耦合相互作用结果有关，在磁园二色谱中还观测到λ＝５８５ｎｍ的强吸收峰     

Phase diagram of the electron-doped La2-xCexCuO4 cuprate superconductor from Andreev bound states at grain boundary junctions

We use quasiparticle tunneling across La2-xCexCuO4 grain boundary junctions to probe the superconducting state and its disappearance with increasing temperature and magnetic field. A zero bias conductance peak due to zero energy surface Andreev bound states is a clear signature of the phase coherence of the superconducting state. Hence, such a peak must disappear at or below the upper critical field Bc2(T). For La2-xCexCuO4 this approach sets a lower bound for Bc2(0) approximately 25 T which is substantially higher than reported previously. The method of probing the superconducting state via Andreev bound states should also be applicable to other cuprate superconductors.     

Superconductivity and field-induced magnetism in Pr2-xCexCuO4 single crystals

We report muon-spin rotation and relaxation (muSR) measurements on single crystals of the electron-doped high-T(c) superconductor Pr2-xCexCuO4. In a zero external magnetic field, superconductivity is found to coexist with dilute Cu spins that are static on the muSR time scale. In an applied field, we observe a mu(+)-Knight shift that is primarily due to the magnetic moment induced on the Pr ions. Below the superconducting transition temperature T(c), an additional source of local magnetic field appears throughout the volume of the sample. This finding is shown to be consistent with field-induced antiferromagnetic ordering of the Cu spins. Measurements of the temperature dependence of the in-plane magnetic penetration depth lambda(ab) in the vortex state are also presented.     

电子型超导体Sm1.85Ce0.15CuO4单晶样品的制备和品质鉴定

本研究了助溶剂法生长了Sm2-xCeXCuO4单晶的可行性，制备出x=0.15,Sm2-x=CexCuO4单晶，并作了品质鉴定，为了研究坩埚中的Al掺入的情况，对电阻率和热电势进行了测量。     

Superconductivity in boron-doped diamond

Superconductivity of boron-doped diamond, reported recently at T(c)=4 K, is investigated exploiting its electronic and vibrational analogies to MgB2. The deformation potential of the hole states arising from the C-C bond-stretch mode is 60% larger than the corresponding quantity in MgB2 that drives its high T(c), leading to very large electron-phonon matrix elements. The calculated coupling strength lambda approximately 0.5 leads to T(c) in the 5-10 K range and makes phonon coupling the likely mechanism. Higher doping should increase T(c) somewhat, but the effects of three dimensionality primarily on the density of states keep doped diamond from having a T(c) closer to that of MgB2.     

溶胶-凝胶法制备Ni_xZn_(1-x)S薄膜的磁性分析

由于离子掺杂可有效改善ZnS薄膜的特性,故本研究以溶胶-凝胶法制备Ni_xZn_(1-x)S薄膜(x=0.00, 0.05, 0.10, 0.15),并利用XRD、PL光谱及磁性测试仪分析Ni掺杂对其磁性的影响.研究结果表明Ni掺杂量x为0.00、0.05、0.10及0.15时薄膜的饱和磁化强度随分别为6.59×10~(-6) emu/cm~3、4.61×10~(-6) emu/cm~3、3.88×10~(-6) emu/cm~3及3.52×10~(-6) emu/cm~3,即饱和磁化强度随x增加而减小. PL分析表明缺陷发光强度随x增加而减弱,能隙发光强度则随之增强,结合束缚极化子理论便知饱和磁化强度会随x增加而减小. XRD分析表示结晶品质随x增加而变好,说明薄膜中的缺陷数量会随x增加而减少,使得磁信号无法通过缺陷方式传导而导致其磁性减弱.     

Enhanced hyperthermia performance in hard-soft magnetic mixed Zn0.5CoxFe2.5−xO4/SiO2 composite magnetic nanoparticles

High quality Zn0.5CoxFe2.5?xO4(x=0,0.05,0.1,0.15)serial magnetic nanoparticles with single cubic structures were prepared by the modified thermal decomposition method,and Zn0.5CoxFe2.5?xO4/SiO2 composite magnetic nanoparticles were prepared by surface modification of SiO2.The magnetic anisotropy of the sample increases with the increase of the doping amount of Co2+.When the doping amount is 0.1,the sample shows the transition from superparamagnetism to ferrimagnetism at room temperature.In the Zn0.5CoxFe2.5?xO4/SiO2 serial samples,the maximum value of specific loss power(SLP)with 1974 W/gmetal can also be found at doping amount of x=0.1.The composite nanoparticles are expected to be an excellent candidate for clinical magnetic hyperthermia.     

Evidence for nodal quasiparticles in electron-doped cuprates from penetration depth measurements

The in-plane magnetic penetration depth, lambda(T), was measured down to 0.4 K in single crystals of electron-doped superconductors, Pr(1.85)Ce(0.15)CuO(4-delta) (PCCO) and Nd(1.85)Ce(0.15)CuO(4-delta) (NCCO). In PCCO, the superfluid density varies as T2 from 0.025 up to roughly 0.3T/T(c) suggestive of a d-wave state with impurities. In NCCO, lambda(T) shows a pronounced upturn for T<4 K due to the paramagnetic contribution of Nd3+ ions. Fits to an s-wave order parameter over the standard BCS range (T/T(c) = 0.32) limit any gap to less than Delta(min)(0)/T(c) = 0.57 in NCCO. For PCCO, the absence of paramagnetism permits a lower temperature fit and yields an upper limit of Delta(min)(0)/T(c) = 0.2.     

effects of rattling phonons on the dynamics of quasiparticle excitation in the beta-pyrochlore KOs(2)O(6) Superconductor

Microwave penetration depth lambda and surface resistance at 27 GHz are measured in high quality crystals of KOs(2)O(6). Firm evidence for fully gapped superconductivity is provided from lambda(T). Below the second transition at T(p) approximately 8 K, the superfluid density shows a steplike change with a suppression of effective critical temperature T(c). Concurrently, the extracted quasiparticle scattering time shows a steep enhancement, indicating a strong coupling between the anomalous rattling motion of K ions and quasiparticles. The results imply that the rattling phonons help to enhance superconductivity, and that K sites freeze to an ordered state with long quasiparticle mean free path below T(p).